Counterbalance for drawing board straightedge



March 26, 1953 R. s. CARDINEYLL 390%,535

COUNTERBALANGE FOR DRAWING BOARD STRAIGHTEDGE Filed April 20, 1959 2 Sheets-Sheet 1 IN V EN TOR. fioleki' CZa rdipeZZ March 26, 1963 R. s. CARDINELL 3,082,535

COUNTERBALANCEZ FOR DRAWING BOARD STRAIGHTEDGE 2 Sheets-Sheet 2 Filed April 20, 1959 United States Patent 3,ti32,535 COUNTERBALANCE FGR DRAWING BQARD STRAIGHTEDGE Robert S. Cardinell, Essex Fells, Nl, assignor to Cardinal! Products, Montclair, NJ, a partnership Filed Apr. 20, 1959, er. No. 867,529 12 fiaims. (Ci. 33-89) This invention relates to balancing devices. More particularly, the invention relates to counterbalances such as are employed to counteract a load in the form of a mass or force.

The invention was occasioned by the need for a suitable counterbalance for drawing board straightedges, and while a counterbalance according to the invention can be used as such in a wide variety of services, it will be described in particular with reference to the use which prompted its discovery.

Drawing boards are commonly formed as the top of a table and are mounted on the table base so that they can be tilted as and when desired to suit the convenience of the draftsrnan. The straightedge is usually cross-string mounted on the board so that as it is moved up and down over the board it is guided in the manner that it remains parallel to the rear and far edges of the board. There is some friction between the string of the mounting and the straightedge and between the straightcdge and board. This friction, however, in general is not sutiicient to suitably stabilize the straightedge when the board is horizontal, and is inadequate to stabilize the straightedge when the board is tilted even a small amount. To facilitale operation of the straightedge there is required some means to stabilize it so that it will retain the position to which it is moved regardless of the extent to which the board is tilted. It has been proposed heretofore to employ a counterweight for this purpose. Broadly, it is the principal objective of the invention to provide a counterbalance which is especially well suited for this service.

Particular objects of the invention are to provide a compact counterbalance which is adapted to be used with all board sizes commonly used and which can be conveniently mounted on the board, and which, when mounted, does not interfere to any objectionable extent with the carrying out of work on the board.

The manner in which these and other objects are attained according to the invention will be apparent from the following description thereof considered in reference to the accompanying drawings wherein a presently preferred embodiment of the counterbalance of the invention is depicted. Since the embodiment of the drawings is merely representative of the invention, reference is made to the appended claims for the metes and bounds thereof.

In the drawings:

FIG. 1 is an isometric view of a drawing board provided with a straightedge and a counterbalance according to the invention;

FIG. 2 is a view of the counterbalance shown in PEG. 1 and viewed from above the counterbalance, with the drawing board disposed vertically;

FIG. 3 is a cross-sectional view taken along line 33 in FIG. 2;

FIG. 4 is a view of the counterbalance shown in HQ. 1 as seen from below, i.e. a bottom View of the counterbalance shown in FIG. 1;

FIG. 5 is a view of the counterbalance of FIG. 1, a portion of the device being broken away, and a portion of the part shown, being indicated in cross section;

FIG. 6 is an enlarged View of a portion of FIG. 5;

FIG. 7 is an enlarged view of the pulley and clutch unit of the device shown in FIG. 2;

FIG. 8 and HQ. 9 are cross-sectional views of the pulley and clutch unit shown in FIG. 7, FIG. 8 showing 2 the clutch engaged and FIG. 9 showing the clutch disengaged; and

FIG. 10 is an exploded view of the pulley and clutch unit shown in FIG. 7.

The counterbalance of the invention employs a spring to counteract weight of the load and advantageously includes a clutch between the spring and the load. One end of the spring is fixed and the other end is connected so that the spring is actuated by manipulation of the load. The actuating end of the spring is linked to the output side of the clutch, and the load is linked to the input side of the clutch, and thus, with the clutch engaged, movement of a counterbalanced load is effective to actuate the spring. The linkage between the output side of the clutch and the actuating end of the spring is adjustable and hence, with the clutch disengaged, the spring load can be changed without adjustment of the position of a counterbalanced load. Thus, the load on the spring for a fixed position of the counterbalanced load can be changed.

In a preferred embodiment of the invention, the spring is of helical form, i.e. the spring is made up of a plurality of axially spaced turns. The helical spring is characterized in that next adjacent turns of the body portion of the spring are in sliding engagement through at least a portion of the working range of the spring. Thus, through a portion of the working range of the spring, adjacent turns thereof are in frictional engagement and hence both the friction between spring turns and energy stored in the spring by winding thereof, eifect operation of the spring. Winding means are secured to one end of the spring and means are provided for restraining rotation of the other end of the spring so that rotation of the winding means about the spring axis is effective to operate the spring through the aforementioned portion of the spring working range. Means in the form of a mechanical linkage are provided for connecting a load to be counterbalanced with the winding means so that movement of the counterbalanced load radially of the spring axis is effective to operate the winding means. Thus, while the spring is in the aforementioned portion of .the working range and a counterbalanced load is connected to the winding means, next adjacent turns of the spring are in frictional engagement and movement of the counterbalanced load radially of the spring axis is yieldingly restrained.

in operation, for example when the counterbalance is employed to balance a drawing board straightedge, the counterbalanced load such as the straightedge will in general be acted upon by a force or forces, usually frictional, in addition and which are independent of the force applied thereto by the counterbalance. The counterbalance of the invention is well suited for cooperation with such forces to provide operation of the system including the counterbalance and load in the manner that the load can be moved through a wide range of positions and will be in static equilibrium in each position within the range.

Advantageously, where the counterbalance is provided with a helical spring, at least one end of the spring is arranged so that it is free to move axially of the spring in response to rotation of the winding means. Such construction permits elongation and contraction of the spring in response to winding and unwinding respectively, and, hence, change in magnitude of frictional engagement between next adjacent turns of the spring incidental to winding and unwinding of the spring is minified.

in FIG. 1, there is shown the combination of a drawing board ll, which is mounted on a base 16 and is provided with tilt adjustment 17, a traightedge 12, and a counterbalance 14 according to the invention. A crossstring mounting 13 is provided for the straightedge and this serves to guide travel of the straightedge over the board. Such mounting is well known in the art so that description thereof in further detail is not set forth here. The counterbalance 14 is secured to the drawing board and is connected to one end of the straightedge by a cable 15. The counterbalance operates in the manner that it stabilizes the position of the straightedge and balances the weight thereof so that the straightedge will remain in the position in which it is placed regardless of the angle of inclination of the board.

The counterbalance 14 has a helical spring 19 characterized in that next adjacent turns of the body portion of the spring are in sliding engagement through the working range of the spring. The spring is a square wire spring, as can be best seen in FIG. 6. Desirably the spring is lightly lubricated with, for example, flake graphite.

A shaft 20 is disposed coaxially within the spring and the spring actuating end 21 is fast to the shaft by connection thereto via end fitting 22 and pin 23. The fast end 24 of the spring 19 is provided with an end fitting 25 and means, shortly to be described, are provided for restraining rotation of the fast end so that rotation of the shaft 20 is effective to wind (or unwind) the spring.

The structure of the end fittings 22 and 25 is indicated in FIG. 6 which is. an enlarged view of end fitting 25. Thus, the end fitting 25, is a tubular element provided with screw threads 31. The end portions of the spring 19 are threaded onto the end fittings and the threads of the fittings are then upset, as is indicated at 32, so that the spring is fixedly secured to the end fittings.

The shaft 20 is journaled in end bearings 26 and 27 which are mounted in spring housing 28. The hon-sing 28 is provided with a tangentially extending flange 29 which facilitates mounting of the counterbalance on a drawing board by means of screws 30. Further, the housing 28 is provided with a slot 33 (see FIGS. 3 and 4) which extends axially of the spring 19 and receives a pin 34 which extends radially outwardly from end fitting 25, to which the fast end 24 of the spring 19 is secured.

As thus far described, the unit operates in the manner that rotation of the shaft 20 is efiective to wind the spring 19 since the spring actuated end 21 is fast to the shaft 20 and rotation of the fast end 24 of the spring is restrained by abutment of the pin 34 with the edges of the slot 33. As the spring is moved through its working range, the fast end 24 thereof moves axially of the spring since the pin 34 is free to travel axially in slot 33. Operation in this manner, as is described hereinbefore, has the advantage of tending to minifiy differences in friction between spring turns for dilferent degrees of winding of the spring.

A pulley 36 is fast to the shaft 20 and rope means in the form of cable 15 is secured at one end thereof, as is indicated at37, to the pulley, and has its other end 33 (see FIG. 1) free for attachment to a load to be counterbalanced and which is disposed radially of the spring, such as the load provided by the straightedge 12 shown in FIG. 1. i

Advantageously, the pulley 36 is mounted on the shaft 20 in the manner that it is detachable, and the counterbalance includes means permitting mounting of the pulley on either end of the shaft. This construction permits mounting the counterbalance on either side of the drawing board (see FIG. 1) depending on convenience. In the embodiment shown in the drawing, the shaft 29 extends beyond each end of the housing 28, providing shaft ends 40 and 41, and the shaft ends are provided with flats 42 so that the pulley knob 50 can be secured to either end of the shaft by means of a set screw 43.

A desirable feature for a counterbalance according to the invention is a clutch operatively interpositioned between the spring and the load to be counterbalanced. Advantageously, the clutch can be incorporated into the mounting of the pulley 36 on the shaft 24 in the manner that the clutch and pulley are assembled as a unit 44 (FIGS. 8, 9 and which is detachable from the shaft 4 and can be mounted on either end thereof according to convenience.

The clutch and pulley unit 44 comprises a tube 45 coaxially mounted over the shaft 20 and having a radially extending flange 46. The pulley 36 is coaxially mounted over the tube 45 and has a radially extending side 47 which is in clutch engagement with the flange 46. As shown in the drawing, a pin clutch can be employed, pins 43, secured to the flange 46, being received in sockets 49 disposed in the said side of the pulley 36. Other types of clutch engagements can of course be employed. A knob 50 is secured to the outside of the tube 45 and across the pulley 36 from the flange 46, and the knob 50 is secured to tube 45 by reason of the plane end 51 of the tube being upset as is indicated at 52. The pulley 36 and knob 50 are provided, respectively, with recesses 54 and 55, and a spring 56 is disposed coaXially of the tube 45 and operatively interposed between the knob 50 and the side 47 of the pulley 36. The spring 56 yieldingly urges the pulley in to clutch engagement with the flange 46. Thus, the clutch is normally engaged and can be disengaged by moving the pulley 36 axially against the force of the spring 56thereon. I

In operation of the counterbalance, the clutch permits changing the load or energization of the spring 19 without alteration of the position of the load which is counterbalanced by the device. In the embodiment shown in the drawing, the clutch input side 47 is integral with the pulley 36 and the clutch output side in the form of flange 46 is fixedly mounted on the shaft 20 by set screw 43. With the clutch engaged so that the pulley is fast to the shaft, movement of the counterbalanced load is effective to actuate the spring by reason of the interconnection of the counterbalanced load and the clutch input side by the cable 15, and the interconnection of the clutch output side and the actuated end 21 of the spring 19, the last mentioned interconnection being by way of shaft 20. With the clutch disengaged, the spring load can be changed by rotating the shaft 20. Rotation of the shaft can be effected by rotation of the knob 50.

Initial adjustment of the device preferably is made by setting the board at an angle of about 30 degrees and increasing spring tension until the counterbalance supports the straightedge. Preferably to avoid damage to the operating elements of the device, the spring is wound only to tighten it, and when it is desired to reduce spring tension or load, the spring is allowed to unwind to the extent desired under its own impulse. Unwinding can be helped along manually but care should be exercised not to force the spring too far in the direction of unwinding.

The counterbalance of the invention is especially useful for the intended purpose of counterbalancing drawing board straightedges. A device having an overall length of 15 inches, a pulley diameter of 2% inches, and employing a square wire helical spring the turns of which are normally in sliding engagement and of length about 9 inches and having about 20 turns per inch, is in general suited for use with any size drawing board, and is operable throughout the range of board inclination or tilt. This general utility of the device is a consequence of the manner of operation thereof and which involves frictional forces inherent in operation of the device, and independent forces such as friction between the straightedge, board and straightedge mounting which provide the straightedge as a restrained load for the counterbalance, and to the combination of these forces. It is also attributable to the provision of means in the form of a manually operated clutch permitting adjustment of spring tension.

An advantage of the device is the convenience with which it can be used. A feature providing this convenience is provision of means for mounting the pulley or pulley and clutch unit on either side of the board. Further, the manner in which the counterbalance and load are interconnected, as is apparent in FIG. 1, pro

vides a counterbalance in the manner that it does not interfere or prevent drawings from extending outwardly from either side of the board, as is frequently a Working condition. Another feature lending to convenience is that the manner provided for adjusting spring tension, i.e. the manually operated clutch, permits adjustment of spring tension while the load is operatively disconnected, due to disengagement of the clutch, from the counterbalance. Thus, it is not necessary to hold the counterbalance against the force of the spring while adjusting spring tension. This is advantageous, particularly in the case of large drawing boards since for large boards, the distance between the device and straightedge at which it is desired to make tension adjustment can be considerable.

Having now described the invention, what is claimed is:

l. A counterbalance comprising a helical spring characterized in that next adjacent turns of the body portion of said spring are in sliding engagement through at least a portion of the workin range of the spring, winding means secured to one end of the spring and rotatable about the spring axis, means for restraining rotation of the other end of the spring in response to rotation of the winding means, whereby the spring can be operated through said portion of the working range by rotation of said winding means, means for connecting a load to be counterbalanced to said winding means for operation of the winding means in response to movement of the counterbalanced load radially of the spring axis, whereby while the spring is in said working range and a counterbalanced load is connected to the winding means, next adjacent turns of the body portion of the spring are in frictional engagement and movement of the counterbalanced load radially of the spring axis is yieldingly restrained, said means for connecting the load to be counterbalanced including a clutch having an input side and an output side, a spring urging said sides to holding engagement, a first interconnecting means connecting the winding means With the output side of the clutch, a second interconnecting means for connecting the input side of the clutch with the load to be counterbalanced, whereby with the clutch engaged movement of the counterbalanced load is effective to actuate the spring, said first interconnecting means being adjustable whereby with the clutch disengaged the spring load can be changed without adjustment of the position of a counterbalanced load.

2. In combination, a counterbalance according to claim 1 and a counterbalanced load operatively connected to said means for connecting a load to be counterbalanced, said counterbalanced load being yieldingly restrained from change in position thereof by a force acting thereon which is independent of the force applied thereto by the counterbalance.

3. A counterbalance comprising a helical spring characterized in that next adjacent turns of the body portion of said spring are in sliding engagement throughout at least a portion of the working range of the spring, said spring having an actuating end and a fast end, a shaft disposed within the spring and coaxially thereof, the actuating end of the spring being fast to the shaft, means connected to the fast end of the spring for restraining rotation of the spring about the shaft, a pulley fast to the shaft, whereby rotation of the pulley is effective to load and unload the spring, rope means having one end thereof fast to the pulley and the other end thereof free for attachment to a load to be counterbalanced which is disposed radially of the spring whereby while the spring is in said working range and a load to be counterbalanced is attached to the rope means, next adjacent turns of the body portion of the spring are in frictional engagement and movement of the counterbalanced load radially of the spring axis is yieldingly restrained, the mounting of the pulley on the shaft including a clutch having an input side and an output side, a spring urging said sides to holding engagement, the clutch input side being fixedly secured 6 to the pulley, whereby with the clutch engaged so that the pulley is fast to the shaft movement of the counterbalanced load is effective to actuate the spring, the clutch output side being fixedly mounted on the shaft, whereby with the clutch disengaged the spring load can be changed by rotating the shaft and without adjustment of position of a counterbalanced load so that the spring load for a fixed position of a counterbalanced load can be changed.

4. In combination, a counterbalance according to claim 3 and a counterbalanced load operatively connected to the free end of the rope means, said counterbalanced load being yieldingly restrained from change in position thereof by a force acting thereon which is independent of the force applied thereto by the counterbalance.

5. A counterbalance according to claim 3, said spring being a square wire spring, said counterbalance including a housin mounted over said spring, said shaft being mounted in the housing for rotation therein, a radially extending pin secured to the fast end of the spring, means defining an axially extending slot in said housing for receiving said pin and permitting axial movement thereof and restraining rotational movement thereof whereby the spring elongates and contracts in response to winding and unwinding, respectively, and change in the magnitude of frictional engagement between next adjacent turns of the spring incidental to Winding and unwinding of the spring is minified.

6. A counterbalance according to claim 3, said clutch and pulley being assembled as a unit, said unit comprising a tube coaxially mounted over said shaft and having a radially outwardly extending flange, said pulley being coaxially mounted over said tube and having a radially extending side thereof, pin means extending between said pulley and tube for efiecting positive clutch engagement therebetween, a knob secured to the outside of said tube and disposed across the pulley from the flange, spring means operatively interposed between said knob and said radially extending side of the pulley and yieldingly urging the pulley into clutch engagement with the flange, whereby the clutch can be disengaged by moving the pulley axially against the force of the spring means thereon.

7. A counterbalance according to claim 6, the clutch and pulley unit being detachably mounted on the shaft, the counter-weight including means for permitting mounting of the clutch and pulley unit on either end of the shaft.

8. A counterbalance comprising a spring having a fixed end and an actuating end, a clutch having an input side and an output side, a first interconnecting means connecting the actuating end of the spring with the output side of the clutch, a second interconnecting means for connecting the input side of the clutch with a load to be counterbalanced, whereby with the clutch engaged movement of a counterbalanced load is effective to actuate the spring, said first interconnecting means being adjustable whereby with the clutch disengaged the spring load can be changed without adjustment of the position of a counterbalanced load so that spring load for a fixed position of a counterbalanced load can be changed.

9. in combination, a counterbalance according to claim 8 and a counterbalanced load operatively connected thereto by connection to said second interconnecting means, said counterbalanced load being yieldingly restrained from change in position thereof by a force acting thereon which is independent of the force applied thereto by the counterbalance.

10. In combination, a counterbalance according to claim 1, a drawing board, a straightedge, and a crossstring mounting for the straightedge secured to the drawing board and connected to the straightedge for guiding travel of the straightedge over the board, said counterbalance being secured to the drawing board and said means for connecting a load to be counterbalanced being operatively connected to one end of the straightedge securing the straightedge as a load on the counterbalance.

'11. A counterbalance comprising a helical spring, a fixed housing enclosing said spring, a shaft coaxially disposed within said spring, one end of said spring being secured to said shaft, a radially-extending pin secured to the other end of said spring, said housing being provided with an axially-extending slot, said pin being received in said slot for axial movement while restraining the rotational movement of the connected end of the spring, whereby the spring elongates and contracts in response to winding and unwinding, respectively, a pulley secured to said shaft whereby rotation thereof is effective to load and unload the spring, and a cable with one end secured to said pulley and the other end free for attachment to a load to be counterbalanced.

12. A counterbalance comprising a helical spring, a fixed housing enclosing said spring, a shaft enclosed by said spring, means fixing one end of said spring to said shaft, means preventing turning of the other end of said spring with respect to said housing while allowing relative axial movement therebetween, a clutch comprising a tube with an outstanding flange at one end and receiving one end portion of said shaft, a knob fitting over said tube and secured against axial movement beyond the unflanged end thereof, a pulley rotatable on said knob and having apertures, pins on'the flange receivable in said apertures, a clutch spring acting between said pulley and knob to urge the pulley toward said flange into a position accepting said pins for placing the clutch in engaged position, set screw means passing through said knob and tube to hold said parts on said shaft, and a cable from said pulley to a load, whereby the stress on said spring may be adjusted, without moving the load, by turning'said knob one way or the other to wind up or unwind said helical spring, after axially moving the knob against the force of said clutch spring to cause removal of the pins from the pulley apertures.

References Cited in the file of this patent UNITED STATES PATENTS 185,804 Wands Dec. 26, 1876 500,046 Ahne June 20, 1893 1,047,801 Haney Dec. 17, 1912 1,658,683 Jacob Feb. 7, 1928 1,922,370 Johnson Aug. 15, 1933 1,975,633 Cakora Oct. 2, 1934 2,226,017 Pixley Dec. 24, 1940 2,518,902 King Aug. 15, 1950 

3. A COUNTERBALANCE COMPRISING A HELICAL SPRING CHARACTERIZED IN THAT NEXT ADJACENT TURNS OF THE BODY PORTION OF SAID SPRING ARE IN SLIDING ENGAGEMENT THROUGHOUT AT LEAST A PORTION OF THE WORKING RANGE OF THE SPRING, SAID SPRING HAVING AN ACTUATING END AND A FAST END, A SHAFT DISPOSED WITHIN THE SPRING AND COAXIALLY THEREOF, THE ACTUATING END OF THE SPRING BEING FAST TO THE SHAFT, MEANS CONNECTED TO THE FAST END OF THE SPRING FOR RESTRAINING ROTATION OF THE SPRING ABOUT THE SHAFT, A PULLEY FAST TO THE SHAFT, WHEREBY ROTATION OF THE PULLEY IS EFFECTIVE TO LOAD AND UNLOAD THE SPRING, ROPE MEANS HAVING ONE END THEREOF FAST TO THE PULLEY AND THE OTHER END THEREOF FREE FOR ATTACHMENT TO A LOAD TO BE COUNTERBALANCED WHICH IS DISPOSED RADIALLY OF THE SPRING WHEREBY WHILE THE SPRING IS IN SAID WORKING RANGE AND A LOAD TO BE COUNTERBALANCED IS ATTACHED TO THE ROPE MEANS, NEXT ADJACENT TURNS OF THE BODY PORTION OF THE SPRING ARE IN FRICTIONAL ENGAGEMENT AND MOVEMENT OF THE COUNTERBALANCED LOAD RADIALLY OF THE SPRING AXIS IS YIELDINGLY RESTRAINED, THE MOUNTING OF THE PULLEY ON THE SHAFT INCLUDING A CLUTCH HAVING AN INPUT SIDE AND AN OUTPUT SIDE, A SPRING URGING SAID SIDES TO HOLDING ENGAGEMENT, THE CLUTCH INPUT SIDE BEING FIXEDLY SECURED TO THE PULLEY, WHEREBY WITH THE CLUTCH ENGAGED SO THAT THE PULLEY IS FAST TO THE SHAFT MOVEMENT OF THE COUNTERBALANCED LOAD IS EFFECTIVE TO ACTUATE THE SPRING, THE CLUTCH OUTPUT SIDE BEING FIXEDLY MOUNTED ON THE SHAFT, WHEREBY WITH THE CLUTCH DISENGAGED THE SPRING LOAD CAN BE CHANGED BY ROTATING THE SHAFT AND WITHOUT ADJUSTMENT OF POSITION OF A COUNTERBALANCED LOAD SO THAT THE SPRING LOAD FOR A FIXED POSITION OF A COUNTERBALANCED LOAD CAN BE CHANGED. 